The US president said the marines "represent a truth that guides our work around the world: when our friends are in need, America helps".

Nepalese rescuers have found three bodies near the wreckage of the US marine helicopter after it disappeared earlier this week, and officials said it is unlikely there were any survivors from the crash.

Mr Obama expressed condolences to the US victims' families during a speech at the National Peace Officers' Memorial Service outside the US Capitol in Washington.

Nepal's defence secretary Iswori Poudyal said: "The wreckage of the helicopter was found in pieces and there are no chances of any survivors." He gave no details about the nationalities of the three victims, only saying their remains were charred.

A separate team sent by the US marines said they had identified the wreckage as the missing UH-1 Huey helicopter.

"The assessment of the site is ongoing and a thorough investigation will be conducted," a statement from the marine-led joint taskforce said.

The wreckage was found about 15 miles from the town of Charikot, near where the aircraft went missing on Tuesday while delivering humanitarian aid to villages hit by two deadly earthquakes, according to the US military joint taskforce in Okinawa, Japan.

The area is near Gothali village in the district of Dolakha, about 50 miles north east of Nepal's capital Kathmandu.

The discovery of the wreckage, first spotted by Nepalese ground troops and two army helicopters, followed days of intense searching involving US and Nepalese aircraft and US satellites.

The US relief mission was deployed soon after a magnitude-7.8 quake hit on April 25, killing more than 8,200 people. It was followed by another magnitude-7.3 quake on Tuesday that killed 117 people and injured 2,800.

The Huey helicopter had been delivering rice and tarpaulins in Charikot, the area worst hit by Tuesday's quake. It had dropped off supplies in one location and was en route to a second when contact was lost.

US military officials said earlier this week that an Indian helicopter in the air nearby heard radio chatter from the US aircraft about a possible fuel problem.

A total of 300 US military personnel have been supporting the aid mission in Nepal, which includes three Hueys, four marine MV-22B Ospreys, two KC-130 Hercules and four US Air Force C-17 Globemaster heavy-lift aircraft.

Lieutenant General John Wissler, commander of the marine-led joint taskforce, told reporters in Kathmandu that his team could not immediately confirm the cause of the crash or identify the bodies found.

"It was very severe crash, and based on what we saw in the condition of the aircraft, we believe there were no survivors," he said.

He added: "Due to the extremely difficult terrain of the site of the mishap, below-freezing temperatures and violent winds and thunderstorms, I made the decision to cease the recovery efforts for this evening. We cannot afford to put US or Nepalese service members at any further risk."

The father of the 31-year-old pilot, Captain Chris Norgren, said marine officials have notified the family that the wreckage was found but have not confirmed the identities of any bodies.